Vapor sensors and smoke detectors, humidity sensors or in general gas sensors are widely used, and the extent of their applicability ranges from industrial or hospital environments and building automation systems to automobile applications or consumer products. Some of these gas sensing systems are based on absorption or sorption of a target gas on a sensing element, which causes a change in the sensing element's properties. These properties are monitored and the changes can be visualized, recorded, or integrated in an automation system. For example, if a sensor detects high concentrations of a determined gas, e.g. CO2, an alarm may be set off.
Some types of sensors utilize the electric properties of a sensing material, which probes the environmental gas by acting as a sorption layer. For example, the sensing material may be an ionic liquid (IL). Ionic liquids are liquids containing or being formed mainly by ions, for example salts in liquid state. ILs are electrically conductive. The resistance of ILs depends on factors such as composition or, notably, viscosity. Upon sorption and dissolution of gas particles in the ionic liquid, the electrical properties of the IL change, hence changing the resistance. In some cases, direct use of ionic liquids as sorption layer may be disadvantageous or even impossible because of flow of the liquid on the sensor surface, and the disability to create thin enough layers, worsening response time. In some cases, the contact area between sorption layer and electrodes may not be constant, and signal may be erroneous or lost. In some cases, conventional systems incorporate the ionic liquid in a gel and producing a thin gel layer as sensing layer in the sensor device. The properties of the IL in the gel, e.g. good analyte solubility and good response in impedance to sorbed species, remain favorable for gas and vapor sensing. Nonetheless, the problem with selectivity and sensitivity remains. Most of the IL-based sensors have low selectivity, because many gasses interact with ionic liquids. This leads to crossed signals, which may result in false reading produced by a mixture of two different gasses. For example, the conductivity of ionic liquids drops with both CO2 and humidity, hence in a wet environment the measurement of CO2 will contain a lot of noise from the environmental water. Moreover, the sensitivity is good only for a limited range in most IL sensors. For instance, humidity sensors may be optimized for either environments with high humidity or with low humidity, and they often fail if the environmental conditions diverge from their optimal range of measurement. It is usually necessary to provide a plurality of sensors, each optimized for a different range, but this is costly and does not solve the problem of cross-sensitivity.